1. Field of the Invention
The present invention relates to an optical imaging method using an adaptive optics system and an optical imaging apparatus including the adaptive optics system. More particularly, the present invention relates to a method for obtaining a fundus image in which an aberration of a subject's eye is measured and corrected.
2. Description of the Related Art
Recently, scanning laser ophthalmoscopes (SLO) which two-dimensionally irradiate a fundus with a laser beam and receive light reflected by the fundus and imaging apparatuses using interference of low-coherence light have been developed as ophthalmologic imaging apparatuses.
The imaging apparatuses using the interference of low-coherence light is called optical coherence tomography (OCT) apparatuses, and is used, in particular, to obtain a tomographic image of a fundus or an area around the fundus.
Various types of OCT, such as time domain OCT (TD-OCT) and spectral domain OCT (SD-OCT), have been developed.
In the ophthalmologic imaging apparatuses, recently, the numerical aperture (NA) of the laser has been increased, and the resolution has been increased accordingly.
However, in the process of obtaining an image of a fundus, the fundus is irradiated with a laser beam through optical tissues, such as a cornea and a lens, of an eye.
As the resolution increases, the influence of an aberration of the cornea and the lens on the quality of the obtained image increases.
Accordingly, researches on adaptive optics SLO (AO-SLO) and adaptive optics OCT (AO-OCT) have been conducted. In AO-SLO and AO-OCT, an adaptive optics (AO) system, which is an adaptive optics system for measuring and correcting an aberration of the eye, is adopted. An example of AO-OCT is described in Optics Express, Vol. 14, No. 10, 15 May 2006, by Y. Zhang et al. In AO-SLO and AO-OCT, a wavefront of an eye is generally measured by a Shack-Hartmann wavefront sensor method.
In the Shack-Hartmann wavefront sensor method, the wavefront is measured by causing measurement light to be incident on the eye and receiving light reflected by the eye with a CCD camera through a microlens array. In AO-SLO and AO-OCT, a high-resolution image can be obtained by driving components such as a deformable mirror and a spatial phase modulator so as to correct the measured wavefront and obtaining an image of a fundus through the components. In an imaging apparatus including the above-described adaptive optics system according to the related art, feedback control is performed by repeating a process of measuring the aberration of the eye for correcting the aberration and a correcting process based on the measured aberrations.
The feedback control is performed to compensate for an error between a command value supplied to a correction device and an actual amount of correction and a variation in aberration caused in accordance with the state of lacrimal fluid and the state of refraction adjustment of the eye.
Similar to general feedback control, in the aberration correction control, it takes a certain time to establish a state in which the aberration is appropriately corrected after the control operation is started.
In particular, since response speeds of the wavefront sensor and a wavefront correction device used to correct the aberration are low, it takes several seconds to several tens of seconds to establish the state in which the aberration is appropriately corrected.